The present invention relates to a device for positioning a member facing each of the perforations of a perforated plate in accordance with a given grid as well as to a process making it possible to remotely fit and dismantle such a device.
More specifically, the invention relates to a device making it possible to position a guide tube in such a way that it faces each of the tubes of a steam generator, such as those equipping nuclear power stations, in order to successively introduce into each of the said tubes a control device, such as an eddy current probe or sensor.
It is known that the tubes of steam generators used in nuclear power stations are exposed to particularly severe operating conditions making it necessary to periodically inspect these tubes in such a way that damaged tubes can be condemned by the sealing of each of their ends. For this inspection to take place, it must be possible to introduce an automatic device into the water box or tank of the steam generator, said device being controlled from the outside. Thus, it is desirable to reduce to a maximum and, if possible, eliminate human intervention within such water tanks, due to the highly irradiated nature of the latter and its small size. For the same reasons, the device must be as reliable as possible and must enable the checking of all the tubes, without any manual intervention being necessary. Moreover, the same requirements make it particularly desirable to construct the device in such a way that it can be remotely fitted and dismantled. Finally, the means ensuring the displacement of the device within the water tank of the generator must, if necessary, enable the jumping of one or more tubes. Thus, the sealed ends of condemned tubes prevent the use of the corresponding perforations of the plate for ensuring the displacement of the device.
A positioning device is known, which comprises two perpendicular arms provided with members permitting their independent fastening into the end of tubes and which can move with respect to one another in three perpendicular directions, so that the guide tubes carried by the arms can be made to face all the steam generator tubes.
This device makes it possible to carry out a complete, remote control inspection in a relatively short time of all the tubes of the steam generator. However, it has the disadvantage that an operator must manually install it in and remove it from the water tank. It must also be equipped with four or even five guide tubes, so as to allow a complete scan of the tube plate. Thus, the equipment permitting the injection of the eddy current probe must be disconnected from one of the guide tubes and connected to another of these tubes when the area to be reached makes this necessary. This operation necessitates a manual intervention, which it would be desirable to prevent for the reasons indicated hereinbefore. Moreover, the displacement of this device does not permit a correct scan of the tube plate when a large number of tubes have been condemned. Finally, the device has a by no means negligible weight, which is not always compatible with the operations to which it is exposed.